The present invention relates to filter cartridges, in particular for internal combustion engines.
More specifically, the invention relates to a filter cartridge comprising a tubular filter element extending along a central axis between two longitudinal ends, said filter element having an external cylindrical surface and an internal cylindrical surface forming a central passage for fluid, said filter element being made from a porous flexible sheet forming a succession of pleats with axial edges, these pleats forming vanes all curved in a same angular direction, each vane comprising first and second portions each having a concave face and a convex face, each of said first and second portions of each vane extending between an inner end close to the internal cylindrical surface of the filter cartridge and an outer end close to the external cylindrical surface oft he filter cartridge, the concave face of the first portion of each van communicating with the central passage and the convex face of the second portion of each vane communicating with said central passage, the first and second portions of each vane being joined at their outer ends, the second portion of each vane being joined to the first portion of an adjacent vane at their inner ends, and the porous sheet having separator elements which hold the different first and second portions of the vanes apart from one another and impart stiffness to said porous sheet.
Document U.S. Pat. No. 2,801,009 describes an example of such a filter cartridge, the disadvantage of which is that it is relatively complex and delicate to manufacture on an industrial scale, particularly since it is difficult to control the exact shape of the curved vanes formed by the pleats of the filter element on a reliable and repetitive basis.
This is made even more difficult due to the fact that the vanes described in the above-mentioned document are made quite rigid because of radial embossing in the filter paper.
The objective of this invention is to alleviate these disadvantages in particular.
To this end, the invention proposes a filter cartridge of the type in question, in which the first and second portions of each vane has hinge lines which are not stiffened by the separator elements and which extend parallel with the central axis of the filter element between the two longitudinal ends of said filter element, said hinge lines sub-dividing each first and second portion of the vanes into at least three panels each having separator elements, and the adjacent panels joined to one another by one of said hinge lines form angles of between 110 and 175 degrees.
As a result of these axial lines forming hinges, the curved shape of the vanes formed by the pleats in the filter element can be better controlled so that the process of manufacturing the filter in made easier and more reliable.
In preferred embodiments of the invention, one and/or other of the following features may be incorporated:
the porous sheet of the filter element has embossments extending along lines perpendicular to the longitudinal axis of said filter element which separate the first and second portions of the different vanes from one another, said embossments being broken by straight compression lines which are adapted not to cause any deterioration in the porous sheet and which form said hinge lines;
the porous sheet has substantially a same thickness at said compression lines and outside said compression lines;
said compression lines are lightly imprinted on the concave face of each first and second portion of the vanes;
the porous sheet of the filter element has stamped embossments which separate the lower faces and the upper faces of the different vanes from one another, said porous sheet having smooth axial strips with no embossing, said axial strips forming said hinge lines;
the porous sheet of the filter element has built-up separator elements which keep the first and second portions of the different vanes apart from one another, said porous sheet having smooth axial strips with no separator element, said axial strips forming said hinge lines;
the built-up separator elements are lines of glue;
the panels bounded by the hinge lines are substantially flat;
the panels. bounded by the hinge lines have a constant or increasing width from one panel to the next, in a radially outward direction;
the second portion of a vane is in contact, through said separator elements, with both the first portion of the same vane and the first portion of an adjacent vane, each adjacent first and second portions thereby delimiting a free space therebetween which forms a substantially constant cross-section between said adjacent first and second portions from the inner end to the outer end thereof, all the lower faces and upper faces oft he filter elements having a substantially identical form and the outer ends of the first and second portions of a same vane being joined to one another by an end face extending substantially parallel with the external cylindrical surface of the filter element;
each second portion of a vane is separate from an adjacent first portion:
by a first curvilinear distance 1 along the internal cylindrical surface of the filter element in a radial plane, which internal cylindrical surface has a first diameter d,
and by a second curvilinear distance L along the external cylindrical surface in said radial plane, which external cylindrical surface has a second diameter D,
the ratio l/L between said first and second distances being substantially equal to the ratio d/D between said first and second diameters;
the end face of each vane of the filter element has a substantially straight cross-section, said end face being joined to the lower face and the upper face of the vane by two axial folds.